Automotive bodies, home electrical appliances and the like have been manufactured with metal materials such as steel sheets, galvanized steel sheets, and aluminum-based metal materials. In general, after being subjected to a chemical conversion treatment step as a pretreatment, a treatment such as coating is carried out. For the chemical conversion treatment, a phosphate treatment is generally carried out. In the chemical conversion treatment with phosphate, a surface conditioning treatment is generally carried out as a preceding process for allowing fine and dense phosphate crystals to be deposited on the metal material surface.
Examples of known surface conditioning compositions for use in such a surface conditioning treatment include treatment liquids containing a titanium phosphate compound referred to as a Jernstedt salt. However, titanium phosphate particles are disadvantageous in that sufficient stability may not be achieved in liquids.
Hence, stable storage for a long period of time in the state of a concentrated liquid has been difficult; therefore, the composition is stored in the state of powder, and a bath is prepared for use by dispersing in a solution. However, for the purpose of simplifying the step, a titanium phosphate-based surface conditioning agent, which would enable storage for a long period of time in the state of liquid, has been desired. In addition, long term stability of the bath has been also desired.
Furthermore, because of such instability, a great influence may be exerted when metal ions such as magnesium ions and calcium ions in tap water contaminate the bath, and result in sedimentation of the titanium phosphate compound. Accordingly, it is necessary to newly prepare the surface conditioning bath in succession.
Moreover, functions per se as a surface conditioning agent could not be considered to be satisfactory. Among metal substrates, some substrates readily cause a chemical conversion treatment reaction, while other substrates hardly cause the reaction. For example, according to conversion resistant metal materials such as aluminum-based metal materials and high-tensile steel sheets, the reaction caused by the phosphate treatment is generally hard to progress, and thus, it has been believed to be difficult to form the conversion coating film in a sufficient amount. Even though such substrates are subjected to a treatment with a treatment liquid including a conventional Jernstedt salt as a principal component, allowing the chemical conversion treatment reaction to progress is difficult. Therefore, a surface conditioning agent having a function to address these conversion resistant metal materials has been desired. In particular, when a surface conditioning agent which can address many kinds of metal substrates can be obtained, many kinds of metals can be subjected to the chemical conversion treatment at once, thereby enabling the chemical conversion treatment to affect a subject composed of many kinds of metal species.
In addition, even in the case of substrates on which the treatment with the Jernstedt salt can be perfected like iron-based substrates and zinc-based substrates, further improvement of the performances is expected by enhancing functions of the surface conditioning agent.
For example, Patent Document 1 discloses a treatment liquid containing the Jernstedt salt, a particular phosphonate salt, and a particular polysaccharide resin. However, the stabilizing effect was not satisfactory even with this treatment liquid, thereby not having enough stability in the state of a concentrated liquid. Rather, functions in terms of surface conditioning may be deteriorated.
Moreover, Patent Document 2 discloses a metal surface activating agent containing titanium phosphate and one or more copper compounds, and further containing phosphoric acid and phosphonic acid. However, stability in the concentrated solution was not considered, and enhancement of the function in terms of surface conditioning was also not considered.
Patent Document 1: Japanese Unexamined Patent Application No. H5-247664
Patent Document 2: Japanese Unexamined Patent Application No. H4-254589